Extrusion coated paper for flexible packaging

ABSTRACT

A barrier laminate for a paper substrate and a pouch formed from the paper substrate is provided. The paper substrate and pouch are suitable for packaging of food products and utilizes a 40-60% hardwood fiber content paper sheet having nylon barriers and EVOH barriers applied to a food contact surface of the paper.

RELATED APPLICATIONS

This application claims the benefit of U.S. Application Ser. No. 62/467,411 filed on Mar. 6, 2017 and which, is incorporated herein by reference.

FIELD OF THE INVENTION

This invention is directed to an extrusion coated paper for flexible packaging such as bags, stand up pouches, and gusseted bags used for food storage.

BACKGROUND OF THE INVENTION

This invention relates generally to the use of flexible packaging for food that is provided to consumers in a flexible pouch or packaging. Many of the pouches for food items involve the use, of plastics and mix substrates and materials that may be difficult to recycle. Additionally, many paper substrates that are utilized for stand up pouches and other items are characterized by poor barrier properties that limit either the shelf life or the ability to package items into a paper pouch. This invention further relates generally to bags and pouches that are typically used to provide for food products. Pouches and similar containers can be used to store a variety of food items. Many embodiments of food storage pouches have one or more gussets that are defined along either a bottom wall or one or more sidewalls. Some gusseted bags have an ability to provide for a “standup” pouch and may further have a transparent window, as part of the gusset, or positioned in a wall panel to allow consumers to see the container contents.

A number of food pouches utilize plastic or foil lined laminated structures. Many such structures are difficult to recycle and are provided from non-sustainable resources. To the extent some pouches are made of paper products, the paper grade is frequently a Kraft type paper and has a low basis weight and strength characteristics which limits its use for certain good packages. The strength of Kraft papers can be increased by the selected use of various barrier coatings. However, the coatings often interfere with the recyclability of the product and the initial low basis weight of the Kraft paper will flex easily which can damage the barrier coatings and result in the lose of needed barrier properties for food items.

Accordingly, there remains room for improvement and variation within the art.

SUMMARY OF THE INVENTION

It is one aspect of at least one of the present embodiments to a pouch for food items comprising or consisting of a tubular structure having upper and lower ends, the upper and lower ends being sealable, front and back walls joined at opposite bag size by at least two side seams running the length of the bags; the bag substrate being paper and having a ground hardwood fiber content of at least about 50%; a food contact barrier coating applied to a first structure of the paper, the barrier coating applied to the first surface of the paper in the order of 5#Nylon, 3#EVOH, 3#Tie, and 17#LDPE.

It is a further aspect of at least one embodiment of this invention to provide a paper substrate comprising of consisting of a paper sheet having an exterior surface and an interior food contact surface; and, a barrier extrusion coating applied directly to the interior food contact surface in the order of 5#Nylon, 3#EVOH, 3#Tie, and 17#LDPE.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A fully enabling disclosure of the present invention, including the best mode thereof to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings.

FIG. 1 is a perspective view of a paper pouch in accordance with one embodiment of the present invention.

FIG. 2 is a perspective view of a paper pouch in accordance with a second embodiment of the present invention.

FIG. 3 is a cross sectional view of an embodiment of a paper substrate laminate of the present invention.

FIG. 4 is a formulation for an anti-curling clay coating.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

It is to be understood that the ranges mentioned herein include all ranges located within the prescribed range. As such, all ranges mentioned herein include all sub-ranges included in the mentioned ranges. For instance, a range from 100-200 also includes ranges from 110-150, 170-190, and 153-162. Further, all limits mentioned herein include all other limits included in the mentioned limits. For instance, a limit of up to 7 also includes a limit of up, to 5, up to 3, and up to 4.5.

In describing the various figures herein, the same reference numbers are used throughout to describe the same material, apparatus, or process pathway. To avoid redundancy, detailed descriptions of much of the apparatus once described in relation to a figure is not repeated in the descriptions of subsequent figures, although such apparatus or process is labeled with the same reference numbers.

It has been found that using a polymer coated ground wood paper for stand up and flat pouches offers significant improvements over conventional paper pouches. The ground wood paper has a higher quality and quantity of hardwood fiber and greater paper basis weight that provides for a stiffer and more rigid container. As a result, the paper is subjected to less flexing and any applied barrier coatings have improved integrity that facilitates a longer shelf life of any perishable item contained therein.

The high ground hardwood fiber content paper also has improved printing capabilities compared to Kraft papers and other similar fiber based substrates. The printing capabilities of the ground wood paper is comparable to print quality obtained for printed publications such as magazines and brochures/catalogs.

In accordance with this invention, it has been found that the use of a clay coated one side (C1S) are a coated-2-side (C2S) paper can be used as a substrate for extrusion coating that offers improvements in the substrate when used for flexible packaging for food items including bags, pouches, gusted bags, and similar articles. As set forth below, it is useful to formulate a clay coating which imparts an anti-curl property to the resulting paper sheet.

When C1S paper is used the polymers are extrusion coated on the non-clay coated side of the paper and the clay coated side is used for printing. C1S paper is preferred in some applications over C2S due to improved polymer adhesion on the uncoated side. In addition, some embodiments use uncoated (UC) paper that does not contain clay coating on either side of the paper. In these embodiments, one side of the paper is extrusion coated with polymers. Then a polymer film or foil layer is attached to the other side of the paper by use of an adhesive or polymer. In case, either standard industry techniques of extrusion lamination or adhesive lamination may be used. It should be noted that it is possible to use a C1S or C2S paper and laminate a polymer film or foil to those substrates as well.

Table 1 shows the properties of the preferred, ground wood containing, base sheet for the invention.

TABLE 1 Properties of TruSpec5 base sheet TruSpec5 Gloss 50# 60# Coating UC C1S Basis weight 50 60 (lbs/3,300 sq. ft) Basis weight 45.5 54.5 (lbs/3,000 sq. ft) Brightness 72 72 Opacity 92 94 Gloss 57 59 Smoothness Top 15.29 21.07 (Sheffield Unit) Smoothness Bottom 22.18 34.87 (Sheffield Unit) bColor 3 3 Ground Wood % 55% 55% Tensile CD (lb/inch) 7.17 8.42 Tensile MD (lb/inch) 23.07 28.96 Tear CD (g/cm) 48.36 62.44 Tear MD (g/cm) 34.93 40.94

Examples of the various embodiments of the invention are provided below. These examples are, intended to illustrate the range of properties that can be covered by the invention. Product attributes, including physical properties and barrier properties, can be adjusted to meet the needs of individual applications by varying the combinations of polymer resins used and the lay downs of individual layers of polymers.

The examples provided have a polymer coat weight of either 28 or 29 lbs/3,000 ft². This was found early in development to be an optimal coat weight from the perspective of product performance and meeting the gauge needs of commercial pouch form and fill equipment. Lower coat weights (to 24 lbs/3,000 ft²) were tested and can be used to meet some applications. A hardwood fiber content of between 40%-65% and more preferably between 50%-60% has proven beneficial.

In accordance with this invention it has been found that the properties of the end substrate are improved using a C1S or an C2C paper in which the clay coating has been modified to prevent or minimize curling of the paper. One suitable formulation for applying, a backwash coating (anti-curling agent) is seen in reference to the formulation given in FIG. 4. Typically, the anti-curl backwash aqueous coating of a kaolin clay and emulsified corn starch is applied to the paper substrate and dried prior to applying an extrusion coating.

Set forth in the various examples below are the extruded composition applied to the indicated paper substrate. Test data is set forth in the various Tables which provide physical properties and performance data of the resulting substrate.

Pouches such as those seen in FIG. 1 have been, prepared from combinations of paper and polymer listed in the examples below and have been found to be able to run at forming rates at commercially useful speeds. For a stand up pouch, a plowed gusset bottom 20 as seen in FIG. 1 can be utilized. In addition, three panel pouches can also be used in which a clear film can be used as the bottom, gusset material to allow a consumer to see the packaged product inside the pouch.

While a variety of suitable films are known in the art, one useful film combination is a 0.5 mil PET/2.0 mil PE film. Another useful film comprises a 0.4 mil PTE/0.1 mil polyuretylene adhesive/0.6 mil nylon/0.1 mil polyuretylene adhesive/3.1 mm polyethylene. Both of the gusset film materials were found to perform well as the bottom gusset in the formation of stand up pouches where the sides are made of a polycoated ground wood paper.

As seen in FIG. 1, a press fit closure 12 can be incorporated into the stand up pouch, the materials and techniques for installing closure 12 being well known in the art.

The coated ground wood paper can also be used to produce flat pouches or pillow pouches for certain food products and with similar barrier properties and benefits to the pouch.

While the representative embodiments evaluated herein are directed to a single gusset pouch with the gusset at the bottom, it is understood that the coated hardwood paper can be used to provide other forms of bags and containers used for food materials. For instance, gussets can be formed one or more of the side walls of a container 10. The coated ground wood paper can also be used to make conventional bags that are typically formed of Kraft paper. For certain items, the bag format allows for a product to be placed in the interior of the bag and the top closure heat sealed.

In addition to the integrity of the ground wood paper, the ground wood paper also lends itself to improved printability and a tactile feel or hand finish that is appealing to consumers. The exterior surface of the pouch and containers can be clay coated as is known in the art for improved printability. The print quality of the resulting pouch is extremely high and is comparable to that obtained from ground wood paper used for printed magazines and catalogs. In addition, consumers are increasingly looking for a biosubstantible package alternative.

As set forth in FIG. 2, is an alternative pouch configuration in an unsealed condition showing opposing layers of two pieces of paper substrate 14 and 16. Optionally, a clear film viewing window 30 can be provided within one or both of the paper substrates to allow viewing of the contents. The manufacturing of such a viewing window within a paper pouch substrate is known in the art as set forth in U.S. Pat. No. 5,465,842 and which is incorporated herein by reference.

Set forth in FIG. 3 is one representative substrate as identified in Example 8 below, that is suitable for use as a paper substrate for forming a pouch, bag, or other similar enclosure for a food product. In the examples below, a similar paper structure can be provided. In the examples that follow, the extruded structure is identified in terms of composition and coating weight and is applied in the order listed to the uncoated surface of the paper substrate.

Example 1

The extruded structure consists of a 29 lb coating of LDPE extrusion coated onto a 60# C1S paper.

TABLE 1 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 LDPE 29 Test Data Burst (bar) 0.21 Side seal strength (gf/in) 2860 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0038 Dart Drop (ft-lb) 0.28 Elmendorf tear MD (grams) 98.7 Elmendorf tear CD (grams) 108.4 OTR 23° C./0% 2798.6 RH (cc/m²day)

Example 2

The extruded structure consists of a 29 lb coating of bioLDPE extrusion coated onto a 60# C1S paper. Note that bioLDPE (i.e. LDPE derived from biobased sources rather than petroleum sources) can be used interchangeably with conventional LDPE for any of the variations in the invention. This substitution has a minimal effect on the properties of the extrusion coated paper.

TABLE 2 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 bioLDPE 29 Test Data Burst (bar) 0.21 Side seal strength (gf/in) 2860 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0038 Dart Drop (ft-lb) 0.28 Elmendorf tear MD (grams) 87.8 Elmendorf tear CD (grams) 106.2 OTR 23° C./0% 2816.8 RH (cc/m²day)

Example 3

The extruded structure consists of a 28 lb coating of a nylon coex structure extrusion coated onto a 60# C1S paper. The coex structure is:

-   -   10# bioLDPE/1.5# tie/5# nylon/1.5# tie/10# bioLDPE

TABLE 3 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 bioLDPE/tie/nylon/ 28 tie/bioLDPE Test Data Burst (bar) 0.26 Side seal strength (gf/in) 3130 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0048 Dart Drop (ft-lb) 0.72 Elmendorf tear MD (grams) 86.1 Elmendorf tear CD (grams) 96.2 OTR 23° C./0% 208.7 RH (cc/m²day)

Example 4

The extruded structure consists of a 28 lb coating of a nylon blend coex structure extrusion coated onto a 60# C1S paper. The coex structure is:

-   -   10# bioLDPE/1.5# tie/5# nylon blend/1.5# tie/10# bioLDPE

The nylon blend consists of 15% amorphous nylon and 85% nylon 6.

TABLE 4 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 bioLDPE/tie/nylon blend/ 28 tie/bioLDPE Test Data Burst (bar) 0.28 Side seal strength (gf/in) 3280 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0049 Dart Drop (ft-lb) 0.65 Elmendorf tear MD (grams) 86.3 Elmendorf tear CD (grams) 107.6 OTR 23° C./0% RH (cc/m²day)

Example 5

The extruded structure consists of a 28 lb coating of a nylon blend coex structure extrusion coated onto, a 60# C1S paper. The coex structure is:

-   -   2# LDPE/1.5# tie/5# nylon blend/1.5# tie/17# LDPE

The nylon blend consists of 15% amorphous nylon and 85% nylon 6.

TABLE 5 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 LDPE/tie/nylon 28 blend/tie/LDPE Test Data Burst (bar) 0.28 Side seal strength (gf/in) 3305 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0048 Dart Drop (ft-lb) 0.56 Elmendorf tear MD (grams) 70.4 Elmendorf tear CD (grams) 85.9 OTR 23° C./0% 128.4 RH (cc/m²day)

Example 6

The extruded structure consists of a 28 lb coating of a nylon blend coex structure extrusion coated onto a 50# UC paper. The coex structure is:

-   -   2# LDPE/1.5# tie/5# nylon blend/1.5# tie/17# LDPE

The nylon blend consists of 15% amorphous nylon and 85% nylon 6.

TABLE 6 Coat weight (lbs/3,000 ft²) UC Paper 45.5 LDPE/tie/nylon 28 blend/tie/LDPE Test Data Burst (bar) 0.27 Side seal strength (gf/in) 2835 Tensile strength MD (MPa) 35 Tensile strength CD (MPa) 13 Puncture (J) 0.0042 Dart Drop (ft-lb) 0.47 Elmendorf tear MD (grams) 73.6 Elmendorf tear CD (grams) 89.6 OTR 23° C./0% 122.5 RH (cc/m²day)

Example 7

The extruded structure consists of a 28 lb coating of a nylon coex structure with metallocene LLDPE blend extrusion coated onto a 60# C1S paper. The coex structure is:

-   -   2#20% mPE-80% LDPE/1.5# tie/5# Nylon/1.5# tie/17#20% mPE-80%         LDPE

TABLE 7 Coat weight (lbs/3,000 ft²) C1S Paper 54.5 mPE-LDPE blend/tie/nylon/ 28 tie/mPE-LDPE blend Test Data Burst (bar) 0.31 Side seal strength (gf/in) 3390 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 15 Puncture (J) 0.0055 Dart Drop (ft-lb) 0.55 Elmendorf tear MD (grams) 71.4 Elmendorf tear CD (grams) 85.5 OTR 23° C./0% 138.8 RH (cc/m²day)

Example 8

The extruded structure consists of a 28 lb coating of a nylon and EVOH coex structure extrusion coated onto a 50# C1S paper. The coex structure is:

-   -   5# Nylon/3# EVOH/3# tie/17# LDPE

The data set forth below with respect to Example 8 and 9 is based on flat sheet samples of the extruded paper product. Performance data on individual pouches formed by the paper substrate is not reported.

TABLE 8 Coat weight (lbs/3,000 ft²) C1S Paper 48.8 nylon/EVOH/tie/LDPE 28 Test Data Tensile strength MD (MPa) 41 Tensile strength CD (MPa) 20 OTR 23° C./0% 0.62 RH (cc/m²day)

Example 9

The extruded structure consists of a 28 lb coating of a nylon and EVOH coex structure extrusion coated onto a 50# C1S paper. The coex structure is:

-   -   5# Nylon/5# EVOH/3# tie/15# LDPE

TABLE 9 Coat weight (lbs/3,000 ft²) C1S Paper 48.8 nylon/EVOH/tie/LDPE 28 Test Data Tensile strength MD (MPa) 43 Tensile strength CD (MPa) 22 OTR 23° C./0% 0.47 RH (cc/m²day)

Example 10

The extruded structure consists of a 29 lb coating of bioLDPE extrusion coated onto a 60# C2S paper with a 1 mil PET film extrusion laminated onto the reverse side.

TABLE 10 Coat weight (lbs/3,000 ft²) bioLDPE 29 C2S Paper 54.5 bioLDPE (adhesive layer 6 for PET film) 1 mil PET film 11.4 Test Data Burst (bar) 0.12 Side seal strength (gf/in) 1186 Tensile strength MD (MPa) 39 Tensile strength CD (MPa) 19 Puncture (J) 0.0147 Dart Drop (ft-lb) 0.82 Elmendorf tear MD (grams) 130.3 Elmendorf tear CD (grams) 194.1 OTR 23° C./0% 46.4 RH (cc/m²day)

Example 11

The extruded structure consists of a 28 lb coating of a nylon coex structure extrusion coated, onto a 60# C2S paper with a 1 mil PET film extrusion laminated onto the reverse side. The coex structure is:

-   -   10# LDPE/1.5# tie/5# Nylon/1.5# tie/10# LDPE

TABLE 11 Coat weight (lbs/3000 ft² ) LDPE/tie/Nylon/tie/LDPE 28 C2S Paper 54.5 LDPE (adhesive layer 6 for PET film) 1 mil PET film 11.4 Test Data Burst (bar) 0.28 Side seal strength (gf/in) 2736 Tensile strength MD (MPa) 40 Tensile strength CD (MPa) 21 Puncture (J) 0.0160 Dart Drop (ft-lb) 0.90 Elmendorf tear MD (grams) 135.6 Elmendorf tear CD (grams) 204.4 OTR 23° C./0% 30.3 RH (cc/m²day)

In addition to the examples listed above, layer multiplication technology (LMT), can be utilized with any of the nylon coex structures presented. Layer multiplication technology allows an increase in the number of layers present in the barrier coatings and which are duplicated in a proportional ratio. Details of the layer multiplication technology useful for the present invention can be seen in reference to the Applicant's co-pending application in PCT/US18/18952, filed Feb. 21, 2018 and which is incorporated herein by reference.

In the various examples set forth above, the described embodiments utilized a nylon coating weight of substantially about 5 pounds. However, it is believed that a range of between 2 to about 8 pounds of nylon can be utilized so as to achieve the benefits as noted herein. Similarly, the coating weight of EVOH is 3 pounds but can be varied between a range of about 1 to about 5 pounds to meet the objectives of the present invention. The coating weights of LDPE or mPE can range between 1-5# when present as an interior layer and between 10-20# when applied as the outermost heat seal layer. The coating weights described above are given in reference to pounds per 3,000 square feet of board as is typically expressed within the industry. Similarly, the basis weight of the paper substrate can vary between a range of 40 to 65 and more preferably within a range of between about 50 to about 60 basis weight.

Although preferred embodiments of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, both in whole, or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions, contained therein. 

That which is claimed:
 1. A pouch comprising: a tubular structure having upper and lower ends, the upper and lower ends being sealable, front and back walls joined at opposite bag size by at least two side seams running the length of the bags; the bag substrate being paper and having a ground hardwood fiber content of at least about 50%; a barrier coating applied to a first structure of the paper, the barrier coating applied to the first surface of the paper in the order of 5#Nylon, 3#EVOH, 3#Tie, and 17#LDPE.
 2. The pouch according to claim 2 wherein the paper has a second surface which is clay coated.
 3. A barrier laminate for a paper substrate comprising: a paper sheet having an exterior surface and an interior food contact surface; a barrier coating applied directly to the interior surface in the order of 2-8#Nylon, 1-5#EVOH, a Tie layer, and 10-12#LDPE.
 4. A barrier laminate for a paper substrate comprising: a paper sheet, having an exterior surface and an interior food contact surface; a barrier coating applied directly to the interior surface in the order of Nylon, EVOH, tie, & LDPE.
 5. The paper substrate according to claim 4 wherein the nylon is present at a range of between 2-8#, the EVOH is present at a range of between 1-5#, the tie layer is present between 1-5# and the LDPE is present between 10-20#.
 6. The paper substrate according to claim 5 wherein the LDPE is a blend of a blend of metallocene LLDPE and LDPE. 